General Description: This Philips TUV 40 watt T5 UV-C germicidal light bulb produces a 253.7 nanometers (nm) light wave which is ideal for water and air purification. It has a slim 5/8 inch (16mm) diameter and is 34 inches long. It has an average life of 9000 hour and will offer the most consistent UV-C output over that period.